A major application of the interconnected block system of the instant invention is to minimize or prevent shoreline erosion from fast flowing water. Such erosion is commonly seen in ocean or seaside environments where wave action can cause significant damage. Similar problems exist where water flowing quickly along a river produces erosion of the river banks. Revetments in the nature of an interconnected block system according to this invention provide excellent erosion protection in such environments while offering other advantages to be discussed hereinafter.
Another area where interconnected block systems, sometimes referred to as geomats or geomattresses, find utility is the capping of dredge spoil domes. Harbors throughout the United States require periodic dredging to maintain sufficient draft depth for shipping. The dredge spoil produced by this operation is loaded into bottom dump barges and transported out to sea to underwater dredge disposal sites which have been identified by the U.S. Army Corps of Engineers.
At the disposal site the dredge spoil material is simply dumped from the barge and allowed to settle to the bottom of the sea at a depth ranging from 150 to 200 feet. This procedure creates large domes of dredge spoil material which range from 1000 to 2300 feet in diameter. The dredge spoil material oftentimes includes contaminated material which is potentially harmful to the environment. A solution is presently being sought to develop ways of capping these domes to prevent migration of the contaminated material to the surrounding ocean beds and water.
One proposed solution for this problem is the use of a concrete mass to cap the domes of contaminated material. There is currently an interconnected concrete block revetment system on the market as described in U.S. Pat. No. 4,370,075, the subject matter of which is incorporated herein in its entirety by reference. In this system, a plurality of individual concrete blocks are cast with horizontally and vertically oriented holes. After the blocks have cured, they are then moved to an assembly area where they are arranged in a selected configuration by hand and steel cables are threaded through the horizontally oriented holes to tie the entire panel together. The panels may then be lifted from the ends of the steel cables by a sling system and positioned for use. The pre-cast vertically oriented holes may be filled with soil to allow for revegetation.
The cables passing through the horizontally oriented preformed holes permit relative movement of the individual blocks. Repeated abrasion resulting from wave action may eventually cause failure of the cables. While the primary function of the cable system is for lifting and placement of the interconnected blocks, destruction of this matrix is believed to significantly reduce the effectiveness of the revetment.
An alternate approach is disclosed in U.S. Pat. Nos. 4,449,847 and 4,502,815, the subject matters of which are also incorporated herein in their entirety by reference. Here, a high strength fabric bag is positioned for use and pumped full of concrete grout. This system is effectively limited to revetment applications and cannot be economically placed in deep water.
Each of these prior art techniques either require placement in situ or by lifting small pre-assembled units. As a result, the size of such installations is relatively small, on the order of, perhaps, forty feet long by about eight feet wide, limiting the use of these systems in efficiently and effectively capping the domes of contaminated dredge material.
More recently, the use of an articulated mat comprising a geogrid embedded in discrete concrete castings has been described in U.S. Pat. No. 5,108,222, the subject matter of which is incorporated herein in its entirety by reference. This system is believed to be severely limited due to the strength of the proposed interconnecting matrix.
An improved approach is disclosed in copending, commonly assigned U.S. patent application Ser. No. 08/455,684 filed May 31, 1995, the subject matter of which is also incorporated herein in its entirety by reference. In the preferred embodiment of that application, a geomattress is formed by placing sections of a uniaxially oriented grid-like sheet material across a plurality of spaced, staggered forms in which the bottom portions of concrete panels have been cast. The uniaxially oriented material includes thickened bars interconnected by oriented strands and the upper portions of the panels are cast to secure at least one such bar to each panel thereby providing a strengthened articulated matrix for interconnecting and supporting the concrete panels during lifting, placement and use of the geomattress.
The aforementioned techniques for producing articulated mats or geomattresses require the concrete blocks to be cast in two separate steps in order for portions of the concrete to pass through the openings of the grid-like matrix. Such a process is time consuming and difficult to accomplish at a construction site. Accordingly, the geomattress must first be formed, then lifted, and transported to a final destination.
Additionally, the need to cast the concrete blocks on both sides of the grid-like matrix so the concrete can pass through the openings and embed the grid material precludes the use of a geocomposite having a geotextile facing adapted for contact with the underlying soil or base material, an important structural characteristic to provide erosion protection, drainage, filtration and separation. Even separately laying a geotextile beneath an interconnected block system of the prior art, a time consuming and labor intensive process, does not adequately and uniformly secure the geotextile in place, limiting the effectiveness of such systems for many applications.
Sorbent material may be used when dealing with contaminated sediments in subaqueous in-situ capping. One of the considerations in designing a cap is the chemical isolation of the contaminated layer, i.e., the design must address the potential for movement of porewater or molecular diffusion from the contaminated layer upward into the cap. Adsorptive materials can be highly effective in reducing the effects of advection and diffusion. This is particularly applicable when groundwater flows up through the bed, such as in a gaining stream, or where consolidation of the contaminated sediment layer is expected to express porewater. Placing the sorbent materials in a stabilized manner in subaqueous conditions is problematic and prior art geomattress constructions have not be useful in efficiently dealing with this problem.
Thus, the prior art interconnected block systems each have limitations in manufacture or use, depending on the particular application for which the products are intended.